JUNE  2007

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563    JUNE 3, 2007:   More to the Solstices Than You Think

We’re finally into June, but not quite to the solstice which begins on the 21st at 2:11 p.m., EDT. The summer solstice for latitudes, at or above the Tropic of Cancer represents the longest day of the year, 15 hours 5 minutes of sunlight for our site of 40 degrees north. The interesting aspect about the solstices is that they only represent the maximum or minimum amounts of daylight, not the extremes of sunrise and sunset. For 40 degrees north, the earliest sunrise occurs on Friday, June 15, when the sun rises at 5:31 a.m. EDT. The latest sunset will happen nearly two weeks afterwards on June 27 when the sun will dip below the horizon at 8:33 p.m., EDT. The Earth will be at aphelion, farthest from the sun, on Friday, July 6 at 8 p.m. about as late as this event can transpire. The times of earliest sunrise and latest sunset never correspond to the solstice dates. Part of this enigma lies in the elliptical orbit of our planet. The daily uniform motion of a fictitious sun rules our civil clocks and gets out of sync with Earth’s changing orbital speed. Earth’s motion around the sun is slowest at aphelion, July 6 this year. Each day, the Earth’s changing orbital position moves the sun eastward by exactly the same angle. By adding four minutes to Earth’s rotational period, we bring the fictitious sun back to the same location each day. The apparent or real sun that we see in the sky is either overcorrected during the summer or under corrected during the winter. The other influence lies in the 23.5 degree tilt of Earth’s rotational plane to its orbital plane. Keep in mind that Earth’s axis is tilted by 23.5 degrees. When the sun has a large northerly or southerly component in its motion, as it does in the spring and fall, its eastward movement is compromised, causing the Earth’s rotation to overcorrect for the sun’s sky location.

564    JUNE 10, 2007:   Solstice Party: Part One

Go pagan and party hardy because the summer solstice is almost upon us. The moment when the sun reaches its most northerly position above the equator, and shines directly upon the Tropic of Cancer, takes place on Thursday, June 21 at 2:11 p.m. The word “solstice” means “sun standstill,” and that is exactly what the sun does on June 21. Daily since the last winter solstice, which occurred early on the 22 of December 2006, the sun has been getting higher in the sky. Each day after the summer solstice, the sun will move lower in the heavens, eventually bottoming on Saturday, December 22 at 1:10 a.m. So if you’re thinking about a solstice celebration, here are a few party tips if you also want a taste of the celestial. Someone should be bringing a telescope. Have several pair of binoculars handy too. This party doesn’t have to start particularly early because the sun does not dip below the horizon until 8:30 p.m. When it does, an interesting array of sky objects await your sighting. By 9 p.m., the nearly first quarter moon dominates in the SW. Its dark, interconnecting seas named Serenitatis, closest to the terminator where the sun is rising; Tranquillitatis (middle), and Fecunditatis were created when huge asteroids slammed into the moon 3.85 billion years ago. That really bright wishing star in the west is Venus. If you scrutinize her carefully, you’ll discover that she has about as much of her surface lit as the moon. Next door is the planet Saturn; its rings are easily visible through even spotting scopes. That faint “star” about two ring diameters away is Titan, Saturn’s largest moon. Huygens, the European Space Agency’s Titan lander, descended into a methane drainage channel on Titan in January of 2005. The celestial treats continue next week for your solstice enjoyment. Read ahead at the URL below.

The locations of Venus, Saturn, the moon, and Jupiter can be seen in the lower right of this all sky map at 9:15 p.m. Above it are renderings showing what the observer might be expected to perceive through a telescope. Gary A. Becker graphics...

565    JUNE 17, 2007:   Solstice Party: Part Two

Some more suggestions follow for your summer solstice party. A telescope and several pairs of binoculars should be handy. High sun occurs this Thursday at 2:11 p.m., but anytime this week would be a great opportunity to celebrate. Last week’s StarWatch contained additional information about the celestial hors d’oeuvres available during the early evening hours. If you go to the URL at the bottom of this page, and click on “this week’s StarWatch,” you’ll find maps which will supplement this text. In addition, large printable maps for all four cardinal directions and the zenith are available by clicking on the appropriate buttons at the top of the page. One planet that space prevented me from mentioning last week was Jupiter, low in the SE by 10:00 p.m. Binoculars held with steady hands and focused precisely, will often reveal one or two of Jupiter’s four large Galilean satellites. A small telescope will easily show all of them: Io, Europa, Ganymede, and Callisto. With higher magnifications, look for the two distinctive equatorial belts on Jupiter. They will appear darker and indicate descending air patterns. The Big Dipper, high in the NW, is already cup down, handle up. Using binoculars, examine the middle star in the handle, and you’ll see two stars close together. They were both born about the same time, but the fainter one, Alcor, is not in orbit around the brighter luminary, Mizar. Mizar, however, is a double star which is easily resolved through small telescopes. Look at Vega, mid-sky in the east. It is the brightest star of the Great Summer Triangle. Near Vega, using binoculars, you’ll see Epsilon Lyrae, two stars of moderate brightness which are, in fact, a double star system. Each star also resolves itself into a double star at higher powers. Bon Appetit and happy summer!

Gary A. Becker graphics...

566    JUNE 24, 2007:   Comet Ferret Charles Messier

Anyone who enjoys viewing the heavens needs to know about Charles Messier (1730-1817), the French observer who cataloged some of most splendid showpieces of the heavens. Messier grew up at a time when the mechanistic universe ruled supreme. Isaac Newton had mathematically quantified gravity, and Edmond Halley, Newton’s friend and adviser, proved posthumously that indeed Newton’s equations could be used to predict the return of a comet, now known as Halley. It was in this spirit of Newtonian theory that Messier came to Paris in 1751 to become a copyist and recorder of observations at the observatory of Joseph Delisle (1688-1768), astronomer of the French Navy. Messier’s passion, however, lay with discovering comets, and he was good at it. Dubbed by Louis XV as the “comet ferret,” Messier’s keen eyes ruled supreme in the harvesting of these solar system interlopers from 1759 through 1780. Star watching from Delisle’s observatory, located in the tower room of the Hotel de Cluny in Paris, Messier used small aperture telescopes. During his searches of the heavens, he chanced upon fixed objects which appeared fuzzy, like distant comets awaiting their discovery. Not wanting to reap the embarrassment for reporting a false sighting, Messier compiled a catalog which eventually grew to 103 members by its final 1781 publication. Messier borrowed from previous listings and later incorporated observations by his protégé and good friend, Pierre Méchain (1744-1804). Later, historians argued that at least seven more objects deserved incorporation into Messier’s list, bringing it to its present total of 110. Messier’s fine assortment of galaxies, nebulae and clusters, known today as “M” objects, will be topics in future summer StarWatch articles.

French astronomer, Charles Messier, left (1730-1817), was dubbed the "comet ferret" by Louis XV (center). In his efforts to find comets, Messier cataloged celestial objects which could be mistaken for distant comets awaiting discovery. Along with Pierre Méchain (1744-1804) and earlier tabulators, Messier's listing of 110 objects contains the finest assemblage of galaxies, globular and open clusters, planetary nebulae, and nebulae in the heavens. Public domain images...